Catalytic cracking process for producing middle distillate

Abstract

A catalytic cracking of hydrocarbons in the presence of an added olefin-containing naphtha increases the selectivity and yield of middle distillate.

What is claimed is: 
     
       1. In a catalytic cracking process wherein a gas oil boiling in the range of about 600° to 1050°F. is converted to lower boiling hydrocarbon products by contacting said gas oil with a cracking catalyst under cracking conditions including a temperature ranging from about 800° to 1000°F. in a conversion zone, the improvement which comprises conducting said contacting step in the presence of an added normally liquid olefin-containing naphtha containing less than about 30 volume percent aromatics, said naphtha containing at least 10 volume percent normally liquid olefins, the volumetric ratio of said naphtha to said gas oil ranging from 20:80 to 40:60, to produce an increased amount of middle distillate components. 
     
     
       2. The process of claim 1 wherein said cracking catalyst is selected from the group consisting of silica-alumina; silica-magnesia and silica-zirconia. 
     
     
       3. The process of claim 2 wherein said catalyst is additionally composited with kaolin. 
     
     
       4. The process of claim 2 wherein said catalyst is additionally composited with a crystalline alumino-silicate zeolite. 
     
     
       5. The process of claim 1 wherein an olefin-containing naphtha is separated from said lower boiling hydrocarbon products and wherein at least a portion of the separated olefin-containing naphtha is recycled to said catalytic cracking zone. 
     
     
       6. The process of claim 1 wherein said olefin-containing naphtha is a naphtha produced by a cracking process. 
     
     
       7. The process of claim 1 wherein said olefin-containing naphtha is a naphtha resulting from a coking process. 
     
     
       8. The process of claim 1 wherein said olefin-containing naphtha is a fraction boiling (at atmospheric pressure) in the range of C 5  to about 300°F. 
     
     
       9. A catalytic cracking process which comprises: a. contacting a gas oil boiling in the range of about 600° to 1050°F. with a silica-magnesia catalyst in the presence of an added normally liquid olefin-containing naphtha fraction boiling in the range of about C 5  to 300°F., said naphtha fraction containing at least 10 volume percent normally liquid olefins, and less than 30 volume percent aromatics, the volumetric ratio of said naphtha to said gas oil ranging from 20:80 to 40:60, to produce lower boiling hydrocarbon products;   b. separating said hydrocarbon products into at least a naphtha fraction boiling in the range of about C 5  to 300°F., and a middle distillate fraction boiling in the range of about 300° to 600°F., and   c. recycling at least a portion of the separated naphtha fraction, without any intervening cracking, to said contacting step (a).